The dioxane which is the subject of this invention is the ordinary dioxane of commerce, otherwise known as 1,4-dioxane and p-dioxane, and has the formula: ##STR1## It has a boiling point of about 101.degree. C. and a melting point of about 12.5.degree. C. It is thus liquid at typical ambient temperatures.
Dioxane is a widely used chemical material. It is soluble in water, and finds extensive utility as an industrial solvent for a large number of chemical substances covering a wide range of polarities. For example, it readily dissolves fats, waxes, natural and synthetic resins, cellulose ethers, and lacquers.
Heretofore, dioxane has been prepared by the acid-catalyzed dehydration of polyethylene glycols. Strong acid catalysts, such as sulfuric acid and sulfonated cation-exchange resins, have been disclosed as suitable for the synthesis of dioxane from polyethylene glycols. Unfortunately, prior methods of dioxane synthesis result in the co-production of significant amounts of an isomeric by-product, 2-methyl-1,3-dioxolane. Purification of the dioxane is difficult, involving tedious and expensive measures for the removal of the isomer. A common method includes refluxing with hydrochloric acid in a current of nitrogen to remove the 2-methyl-1,3-dioxolane, drying with potassium hydroxide, refluxing with metallic sodium, and finally distilling from sodium.
For some uses, the purity of the dioxane must be very high. For example, when used in spectroscopic and scintillation analysis, or as a reaction medium for organometallic chemistry, the dioxane concentration must be as close to 100% as possible. The presence of the isomeric dioxolane is especially a problem when high purity dioxane is sought for these applications.
It would therefore be desirable to have a procedure for the preparation of dioxane which does not involve the formation of the troublesome isomeric by-product and which instead produces a crude reaction product from which the dioxane can be isolated relatively easily to achieve a high purity product. It has now been found that dioxane can be synthesized from polyethylene glycols in accordance with the present invention as hereinafter described, without the formation of the isomer 2-methyl-1,3-dioxolane. By the invention herein, dioxane is formed along with co-products from which the dioxane can be readily separated and recovered in highly pure form.
One of the by-products of the novel process of this invention is the compound 5-ethyl-2-methylpyridine having the formula: ##STR2## This alkylpyridine is useful in the production of the important B-complex vitamin niacin and in the production of oil-resistant synthetic rubbers. 5-Ethyl-2-methylpyridine has previously been prepared from acetaldehyde or paraldehyde and ammonia. Hence, the present invention also provides a novel method of making this valuable pyridine derivative which can be separated from the dioxane and isolated in a relatively pure state.
Accordingly, a principal object of the present invention is to provide a method for the preparation of dioxane and valuable co-products. A further object is to provide a method for preparing dioxane in high purity without having to utilize difficult purification techniques.
Another object of the present invention is to provide a composition containing dioxane and 5-ethyl-2-methylpyridine. A further object of the present invention is to provide a method of treating a composition containing dioxane and 5-ethyl-2-methylpyridine to isolate these respective compounds in relatively pure form.
Still another object of the present invention is to provide a reaction medium for the conversion of polyethylene glycols to dioxane and 5-ethyl-2-methylpyridine.
These and other objects of the present invention which will be apparent hereinafter are obtained by the present invention which resides in the compositions, compounds, materials and processes described herein.